The present invention relates generally to semiconductor fabrication techniques and devices thereof. The present invention also relates to ion implantation methods and systems. The present additionally relates to extraction electrodes utilized in ion implantation methods and systems.
In semiconductor manufacturing, ion implantation is primarily utilized to introduce dopant ions into silicon wafers. This can be accomplished by generating, in an ion implanter, a gas plasma such that the resultant particles can be accelerated under the influence of electric field, and directed onto a semiconductor substrate for implantation to a desired depth beneath the surface of the substrate. Because of its superiority over chemical doping, ion implantation has largely replaced diffusion (chemical) doping in an increasing number of VLSI (very large scale integration) applications.
Semiconductor fabrication processes often utilize a high current ion implantation machine to implant impurity ions into semiconductor substrates in order to form doped regions, such as sources and drains. The ion implanter delivers a beam of ions of a particular type and energy to the surface of a silicon substrate. Such machines typically include an ion source supply, normally a gas source, and an ion source power supply which is connected to an ion source head. A small quantity of the gas is passed through a vaporizer oven and then into an arc chamber which includes a heated filament, and an anti-cathode.
The filament can be directly heated by passing electric current through it, derived from the power supply. This heating causes thermionic emission of electrons from the surface of the filament. An electric field (e.g., 30 to 150 volts) can be applied between the filament and the arc chamber walls utilizing the power supply. The field accelerates the electrons in the filament area to the arc chamber walls. A magnetic field can then be introduced perpendicular to the electric field, thereby causing the electrons to spiral outward, increasing the path length and chances for collisions with the gas molecules. The collisions break apart many of the molecules and ionize the resultant atoms and molecules by knocking outer shell electrons out of place.
As charged particles, these atomic or molecular ions can now be controlled by magnetic and/or electric fields. Source magnets can be utilized to alter the ion path from, for example, a straight path to a helicoid path. With one or more electrons missing, the particles generally carry a net positive charge. An extraction electrode (anti-cathode) placed in proximity to a slit and held at a negative potential attracts and accelerates the charged particles out of the chamber through the slit opening in the top of the chamber. Ions exiting the chamber are passed through an acceleration tube where they are accelerated to the implantation energy as they move from high voltage to ground. The accelerated ions form a beam well collimated by a set of apertures. The ion beam is then scattered over the surface of a wafer using electrostatic deflection plates.
Thus, ion implantation techniques can be utilized for the placement of ions in a semiconductor material such as a silicon substrate at precisely controlled depths and at accurately controlled dopant concentrations. One of the major benefits of the ion implantation method is its capability to precisely place ions at preselected locations and at predetermined dosage. It is a very reproducible process that enables a high level of dopant uniformity. For instance, a typical variation of less than 1% can be obtained across a wafer.
An ion implanter typically operates by providing an ion source wherein collisions of electrons and neutral atoms result in a large number of various ions being produced. The ions required for doping are then selected out by an analyzing magnet and sent through an acceleration tube. The accelerated ions are then bombarded directly onto the portion of a silicon wafer where doping is required. The bombardment of the ion beam is usually conducted by scanning the beam or by-rotating the wafer in order to achieve uniformity.
A heavy layer of silicon dioxide or a heavy coating of a positive photoresist image is used as the implantation mask. The depth of the dopant ions implanted is dictated by the energy possessed by the dopant ions, which is normally adjustable by changing the acceleration chamber voltage. The dosage level of the implantation, i.e., the number of dopant ions that enters into the wafer, is determined by monitoring the number of ions passing through a detector. As a result, a precise control of the junction depth planted in a silicon substrate can be achieved by adjusting the implantation energy, while a precise control of the dopant concentration can be achieved by adjusting the dosage level.
One of the difficulties involved in ion implantation involves the use of an extraction electrode, which was previously mentioned. It is very difficult to tune an ion beam without a properly positioned extraction electrode. Because such an extraction electrode is usually located at a first slit beyond an associated source head, the extraction electrode determines the path by which a magnet thereof directs the ion beam path.
Thus, it is extremely important to be able to monitor the position of the extraction electrode. It also important to be able to monitor the extraction electrode in xe2x80x9creal timexe2x80x9d and thereby avoid potential problems that may arise following a typical ion implantation procedure. Present extraction electrode systems do not permit sufficient monitoring of the extraction electrode, particularly in real-time. Prior art systems and methods thereof simply do not permit accurate monitoring of such extraction electrodes. The present inventors have concluded, based on the foregoing, that a need exists for a method and system which can overcome the aforementioned problems associated with the prior art.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is therefore one aspect of the present invention to provide an improved semiconductor fabrication method and system.
It is another aspect of the present invention to provide an improved ion implantation method and system.
It is still a further aspect of the present invention to an improved method and system for monitoring an extraction electrode utilized in ion implantation operations.
The above and other aspects of the present invention can thus be achieved as is now described. A method and apparatus are disclosed herein for monitoring an extraction electrode utilized in the ion implantation of charged particles on a semiconductor wafer. A signal may be generated from an encoder associated with the extraction electrode, wherein the signal comprises data indicative of charged particles attracted to and accelerated by the extraction electrode. The signal may then be analyzed either manually or automatically to determine if the extraction electrode is located at a position appropriate to attract and accelerate the charged particles to an acceleration tube for proper implantation thereof upon the semiconductor wafer. A main controller may be linked to the extraction electrode, wherein the main controller controls a location of the extraction electrode in proximity to the charged particles. Such a controller may be a Programmable Logic Array (PLC). The position of the extraction electrode can be indicated utilizing a light emitting diode (LED). In general, a lead out signal can be provided from the encoder. A PLC may be utilized to communicate a high-voltage signal with a main controller.
The present invention thus discloses a monitoring apparatus and method for an extraction electrode utilized in an ion implanter. Such a monitoring apparatus, can include a motor equipped with an output shaft, and an extraction electrode fixedly attached to a first end of a screw rod. Additionally, such a monitoring apparatus may include a first drive device for transmitting motion form the output shaft of the motor the screw rod for providing rotational motion of the extraction electrode. The monitoring apparatus also incorporates a conversion device for converting mechanical movement of the extraction electrode into an electronic signal, the conversion device comprising a coder equipped with an input axle. Finally, such a monitoring apparatus also generally includes a second drive device for transmitting motion from the output shaft of the motor to the input axle of the conversion device for coding thereof by the coder based on the rotational angle of the input axle.